Kevin Ryan, a member of law firm Epstein Becker & Green, said it's not surprising that there hasn't been as much enforcement of Medicare Part D fraud as there has with other parts of Medicare before now because the program is relatively new. Medicare Part D was implemented in 2006.

"I think you can expect enforcement in all parts of Medicare, and the fact that there's now been major enforcement in Part D just goes to show you there are not sections or parts of Medicare that are exempt from enforcement when it comes to fraud,” Ryan said.